The proposed research addresses two long-term goals: l) Our major goal is to develop a better understanding of the functional organization of the human visual system, using comparative data from our studies on monkeys as a major source of new information. We want to know how the visual system is subdivided into areas and nuclei, how areas and nuclei are composed of modules and layers, and how modules, areas, and nuclei are interconnected into processing networks. We plan to study both New and Old World Monkeys because New World Monkeys offer significant technical advantages in testing some hypotheses, Old World Monkeys are more closely related to humans, and features common to the visual system of both groups are more likely to be present in humans. Studies will combine electrophysiological, histochemical, architectonic, and connection-tracing methods to test specific hypothesis generated from previous observations and theories. The emphasis will be on visual and visuomotor cortex, including polysensory areas, but pulvinar organization will also be considered. 2) Related studies will evaluate the effects of deactivating specific visual structures or parts of structures on the responsiveness of neurons in other parts of the visual system to visual stimuli. These studies relate to two separate goals. First, the immediate effects of such deactivations will test hypotheses based on connectional anatomy of how information is processed. Are particular connections essential or important in the neural activity of a given cortical area? Second, determining the immediate and long-term effects of deactivation will allow us to test hypotheses about the location, extent, and significance of plasticity in the mature visual system. More specifically, is information lost after a partial lesion of a cortical visual area later recovered in a process of retinotopic reorganization? These studies will provide a better understanding of the functional consequences of damage to the human visual system, and the potential for recovery. They may also provide a conceptual framework for the design and implementation of therapeutic measures.